She once ran a snake cult in the Tashalar and her specialty is magics that can link together spells in a sort of chain contingency spell trigger set up. Hence Elminster is wary of slaying her out of hand (and might have a tough time of it, she appears powerful) as he does not know what ramifications (in terms of blasting spells going off everywhere throughout faerun) this might have.
History[]
The Company of Crazed Venturers ran across her and ended up confronting her on a small island of the Sword Coast. To show their "power" one of the Company mages disintegrates (as per the spell) a small pebble. Shaan bends down, touches the island and disintegrates it, leaving the Company floundering in icy water while she calmly flys off.
Imprisoned in the Floating Helm of Tharados